What delay is FP?

[RLangham]

So I get what FP sync does. I've never seen any FP bulbs but I know what the deal is with them.
But unlike say M or F sync, I can't find anywhere online where it gives a figure for the delay used with FP. Most of my cameras have an FP socket and I want to know if there's any way to use FP sync at speeds below X speed with M or F bulbs (I have some Press 25's, for instance.)

So what's the delay in milliseconds?

 

[BrianShaw]

https://lommen9.home.xs4all.nl/GRAFLITE/page2.html

https://filmphotographyproject.com/content/howto/2018/07/flash-bulbs-lowdown/

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[Donald Qualls]

The idea of the FP sync is to fire a special Focal Plane flashbulb. This bulb, with a near-flat light curve over a 1/8 second or slightly longer burn time, was intended to provide even light during the entire travel of a large format focal plane shutter (Graflex RB, Speed Graphic, etc.). There's no way to effectively use it with modern flash or late-generation flashbulbs, because it fires the flash some tens of milliseconds before the first curtain starts to open (to let the bulb come up to brightness), and then that's it. Your M2 bulb, never mind your strobe, will be all over before any of the film is uncovered by the slit in the curtain.

 

[RLangham]

The idea of the FP sync is to fire a special Focal Plane flashbulb. This bulb, with a near-flat light curve over a 1/8 second or slightly longer burn time, was intended to provide even light during the entire travel of a large format focal plane shutter (Graflex RB, Speed Graphic, etc.). There's no way to effectively use it with modern flash or late-generation flashbulbs, because it fires the flash some tens of milliseconds before the first curtain starts to open (to let the bulb come up to brightness), and then that's it. Your M2 bulb, never mind your strobe, will be all over before any of the film is uncovered by the slit in the curtain.

Well here's the thing, though. The actual delay before it fires the shutter is apparently similar between M sync (which my cameras don't have) and FP sync, according to that link. Now, some of my cameras have automatic switching or have FP disabled at speeds below X-sync, but some of them don't. For instance my srT 101 will happily still close the circuit across the FP terminal at speeds below 1/60th. Since the delay time is within a few milliseconds of the same, using a speed of 1/60th, I should be able to treat the FP terminal as if it were an M terminal.

 

[BrianShaw]

What camera? What shutter?

 

[RLangham]

What camera? What shutter?

Let's say Minolta srT focal plane shutters and... Nikkormat FtN has an FP terminal as well, doesn't it? Or does it just have X and F?

 

[BrianShaw]

It might actually work, but since the M bulbs are not “flat burning” your exposure could vary as the shutter slit crosses the film. You should map your shutter speeds against the burn pattern of the bulb you will be using to see how uneven it will be

Alternative: buy FP bulbs. I saw a case on eBay Not an inexpensive option but...

 

[RLangham]

It might actually work, but since the M bulbs are not “flat burning” your exposure could vary as the shutter slit crosses the film.

The shutter will be entirely open for a little under 1/60th of a second at 1/60th, so there will be no slit as such. If the flash comes soon enough to be in that window it will expose the frame evenly.
I agree that I may have to go down to 1/30th to extend that window. I'm used to cameras that have x-sync only at 1/30th, though. It does make the high intensity flash bulbs I have a little less useful, since they're for flash fill in bright daylight, with foot guide numbers in the hundreds.

 

[BradS]

Here is a user manual for the Nikkormat FS (a meter-less FTN) that I found on the Nikon website (google is your friend).
See page 22 for flash sync info....

Nikkormat FS User Manual PDF

 

[RLangham]

Here is a user manual for the Nikkormat FS (a meter-less FTN) that I found on the Nikon website (google is your friend).
See page 22 for flash sync info....

Nikkormat FS User Manual PDF

I mean, I own an FTn, I just wasn't near it to see what the second terminal says. I think it's F now that I think of it.

Anyways, M. Butkus should have the actual FTn manual, his Nikon section is very exhaustive.

 

[Donald Qualls]

The shutter will be entirely open for a little under 1/60th of a second at 1/60th, so there will be no slit as such. If the flash comes soon enough to be in that window it will expose the frame evenly.

That might work -- most common M-sync bulbs burn for about 1/40 second -- but the problem you might have is that the rear curtain will be traveling when the bulb's burn starts to tail off significantly; that will mean part of the frame will get less exposure. If you slow your shutter to 1/30, at least the bulb should burn out completely before the rear curtain releases.

 

[BradS]

Oh for heaven's sake! Here...here's the page from the FTN manual.

 

[BradS]

and here are some spotmatics...

 

[RLangham]

That might work -- most common M-sync bulbs burn for about 1/40 second -- but the problem you might have is that the rear curtain will be traveling when the bulb's burn starts to tail off significantly; that will mean part of the frame will get less exposure. If you slow your shutter to 1/30, at least the bulb should burn out completely before the rear curtain releases.

I wonder how fast the shutter curtains travel on that camera. I know that the delay timer comes into play at 1/60th (you can hear it on some examples when you turn the dial to that position) which implies that an opening wide enough to give an exposure of 1/60th without the timer would be too wide. This implies that the shutter has fairly fast curtains compared to some cameras, where 1/60 is just a slit somewhat wider than the film gate, with no delay. This actually implies that, had they had the desire, they could have put an additional shutter speed of circa 1/80 or 1/90, which would be just below the actual x speed of the camera and thus fully synchronized (this is the case for the Nikon F2).

I wish I knew the travel time of the first curtain so I knew how long it would actually be on a well-calibrated example between fully open and the beginning the second curtain closure.

 

[RLangham]

Oh for heaven's sake! Here...here's the page from the FTN manual.

View attachment 255613

That's interesting. The large slits and short travel times of the vertical shutter seem to allow many kinds of flashbulbs to act like FP bulbs.

On the other hand it seems like the cloth curtains don't want to sync an M bulb at very high speed at all. A test is in order I think.

 

[Donald Qualls]

That's interesting. The large slits and short travel times of the vertical shutter seem to allow many kinds of flashbulbs to act like FP bulbs.

On the other hand it seems like the cloth curtains don't want to sync an M bulb at very high speed at all. A test is in order I think.

I see the same page saying you can use M bulbs at any shutter speed when using the M sync connector. So yes, acting like FP bulbs without needing an actual FP bulb. Apparently the slit travel time is within the bulb's "flat" brightness time.

 

[RLangham]

I see the same page saying you can use M bulbs at any shutter speed when using the M sync connector. So yes, acting like FP bulbs without needing an actual FP bulb. Apparently the slit travel time is within the bulb's "flat" brightness time.

These early all-mechanical Copals are some of the best shutters ever made. They last forever and they don't typically take damage if the camera gets dropped or banged into something.
My Nikkorex F should have the same flash sync characteristics.

 

[BrianShaw]

I once had to remove sticky semi-molten light trap material from one. It wasn’t easy and I couldn’t believe that after rough treatment like that the shutter worked fine.

 

[Donald Qualls]

Same is also true of all my M42 cameras except my actual Spotmatic -- they're all fully mechanical Copal Square. That, plus the glass and the fact it's all long paid for and not battery dependent, is why I'll never replace my M42 bodies and lenses.

I do have one body that demonstrates that a finger in the blades will damage a Copal Square, though... No, it wasn't my finger.

 

[RLangham]

Same is also true of all my M42 cameras except my actual Spotmatic -- they're all fully mechanical Copal Square. That, plus the glass and the fact it's all long paid for and not battery dependent, is why I'll never replace my M42 bodies and lenses.

I do have one body that demonstrates that a finger in the blades will damage a Copal Square, though... No, it wasn't my finger.

I had a Yashica TL Electro X that had one of Copal's first electric shutters. It worked great (for a step-down camera) until some idiot spilled soda on it.

 

[Dan Fromm]

Hmm. The higher the shutter speed, the lower the flash's Guide Number.

With focal plane shutters, M class sync fires the bulb 20 milliseconds before the shutter opens. With leaf shutters it fires the bult 20 ms before the shutter is fully open.

With F class sync, the delay is 5 ms.

 

[RLangham]

Hmm. The higher the shutter speed, the lower the flash's Guide Number.

With focal plane shutters, M class sync fires the bulb 20 milliseconds before the shutter opens. With leaf shutters it fires the bult 20 ms before the shutter is fully open.

With F class sync, the delay is 5 ms.

Yes, for instance, Press 25 has a guide number of 140 ft. at ASA 100 and 1/750. Hence at 20 ft. I would select F/8 or so.

 

[Donald Qualls]

Yes, for instance, Press 25 has a guide number of 140 ft. at ASA 100 and 1/750. Hence at 20 ft. I would select F/8 or so.

And don't forget to warn all your subjects to stand still after the flash, until they can see again...

 

[shutterfinger]

Years ago (5-10ish) there was a site called Dons Bulbs. It went the way of the Dodo but you may be able to find it on the Wayback archive.
In the libruary were catalogs of flashbulbs from several manufacturers.
Type M flash bulbs take 15 to 17 milliseconds to reach 2/3 of peak output and burn for 20 milliseconds before the light output drops below 2/3 of peak output, the usable light output range of the bulb.
Type FP flash bulbs take the same 15 to 17 milliseconds to reach 2/3 of peak then burn for 50 milliseconds before droping below 2/3 of peak output. The shutter travel time of 4x5 Graflrx SLR's is 42 to 48 milliseconds depending on speed selected.
Type F flash bulbs take 5 milliseconds to reach 2/3 of peak and burn for 15 milliseconds before droping below 2/3 of peak.
The Pentax Spotmatic Service manual states the curtaun travel to be adjusted to 14 ± .3 millisecond. This should be ballpark correct for other horizontal travel focal plane shutters in 35mm cameras.

 

[Dan Fromm]

The Pentax Spotmatic Service manual states the curtaun travel to be adjusted to 14 ± .3 millisecond. This should be ballpark correct for other horizontal travel focal plane shutters in 35mm cameras.

This surprised me so I looked up the Spottie's highest electronic flash sync speed. 1/60. Yikes! Copal Square shutters sync at speeds up to 1/125. Some newer 35mm SLRs' shutters sync at up to 1/250. Are there faster ones? Name names, please, and give numbers.